Operators of bulk liquid cargo ships and barges (tankvessels), have come under increasing pressure to avoid polluting spills when casualties such as collisions and groundings occur. The cargo tanks of tankvessels are formed by intersecting longitudinal and transverse bulkheads which divide the hull of the vessel into independent tanks. The hull forms the bottom of the tanks and, on the side tanks (known as wing tanks), one side of the tank. There is a movement, particularly in the United States, to require all tankvessels to at least have plating inside of and spaced from the bottom of the hull to form void spaces beneath the cargo tanks in the vessel (double bottoms). Such requirements have been resisted for a variety of reasons, not the least of which includes the reasoning that double bottoms will not actually protect the cargo since most penetrations of the hull are of such a nature that the double bottom will be at least fractured by the hull penetration. Another disadvantage of double bottoms is that the void spaces formed thereby create collection points for vapors thereby generating an explosion hazard. Other obvious disadvantages of double bottoms are that they add weight to the vessel and cost to its construction, cut down on the cargo carrying capacity of the vessel and are impossible to reasonably retrofit in existing tankers.
A fact of the geographical situation of the Middle East oil producing nations is that, although rich in oil, they are poor in potable water. Potable water is expensive to produce and various schemes, such as towing iceburgs from the Antarctic, have actually been seriously considered to remedy the situation. These nations are in need of potable water, from whatever source it can be economically provided.